Exam 200-301 topic 1 question 467 discussion

ref BW 100000 MB ref BW BW G0/0 100000MB divided by 10000MB (or 10000000KB) = 10 cost G0/1 100000MB divided by 100000MB (or 100000000KB) = 1 cost

Answer should be A. Ref-bandwidth / bandwith = ospf cost note that bandwidth is in kilobits per second, so you need to convert to Mbs to get the accurate cost.

B is correct G0/0 is 100000000Kb/10000000Kb = 10 G0/1 is 100000000Kb/100000000kB = 1

Three things are true: 1. The "auto-cost reference-bandwidth" takes its argument in Mb. 2. The "bandwidth" command takes its argument in Kb. 3. The formula for calculating OSPF cost is reference_bandwidth/interface_bandwidth. Converting to Kb, the reference-bandwidth is 100000000Kb. The cost calculations are then as follows: G0/0 = 100000000Kb/10000000Kb = 10 G0/1 = 100000000Kb/100000000kB = 1 G0/1 has the lowest cost. The answer is B.

Recall: > Cost = (10^6 bps * reference-bandwidth)÷(link-bandwidth) > The "bandwitdh" command will assign bandwidth in [kbps]. G0/0: Cost = (10^6 bps * 10^5 bps)÷(10^7 bps * 10^3) = 10^1 = 10 G0/1: Cost = (10^6 bps * 10^5 bps)÷(10^7 bps * 10^3) = 10^0 = 1 G0/2: Cost = 100 (set by-> ip ospf cost command) G0/3: Cost = 1000 (set by-> ip ospf cost command) > Therefore: The lowest route path cost is connected to the G0/1 (cost = 1).

The Cost formula is reference bandwidth divided by interface bandwidth. To adjust the reference bandwidth, use the auto-cost reference-bandwidth Mb/s router configuration command. To adjust the interface bandwidth, use the bandwidth Kb/s interface configuration command. A. 10 B. 1 C. 100 D. 1000

ANSWER is b, since the bandwidth value is altered for g0/0 & g0/1, the bw value for them are in kb. first divided them by 1000 to get the values in MB. second, now divide the ref bw value/ interface bw values the cost for g0/1 would be 1, which is lowest.

bandwidth (BW) is expressed in kbps. cost = 100 Mbps/BW cost Ge0/0 = 1/100 cost Ge0/1 = 1/1000 cost Ge0/2 = 100 cost Ge0/3 = 1000 Answer is B: Ge0/1 has the lowest cost

This is a trick question, both G0/0 and G0/1 have a cost of 1 In OSPF if the interface has a higher bandwidth than the cost metric it will be 1. The answer is indeterminate between A and B

it cannot be A as B has a higher Bandwidth

to expand to what g_mindset said: OSPF's metric is called "cost". When you change an interface's bandwidth, it's in kilobits #R1(config-if)#bandwidth ? <1-10000000> Bandwidth in kilobits It's in kilobits. We can tell G0/0 and G0/1's bandwidth were manually altered because 'auto-cost reference bandwidth' was set to 100000 (it's different). A router's cost reference bandwidth is default 100mbps. This is what it looks like when you change the auto-cost reference bandwidth: Router(config-router)#auto-cost reference-bandwidth ? <1-4294967> The reference bandwidth in terms of Mbits per second It's it Mbits per second. Reference-Bandwidth(Mbps) / Interface Bandwidth(Mbps) = OSPF cost 10000000kbps / 1000(Mbps (intG0/0's)) = 10000 10000 / 1000 = 10 Interface GigabitEthernet0/0 has a cost of 10.

B is correct because int g0/1 has a higher bandwidth configured than int g0/0 and therefore a lower cost.